A conventional automotive radiator has a tubular member which is connected to a filler neck formed on an upper tank, as shown in Japanese patent laid-open publication (KOKAI) No. 55-41391, a radiator cap which has both negative pressure valve and a pressure valve connected to the tubular member and a connecting pipe connected with the tubular member so that the tubular member is connected with a reserve tank through the connecting pipe.
The pressure valve of the radiator cap opens in order to release super heated steam within the upper tank to the reserve tank when the pressure within the upper tank increases up to the predetermined pressure.
Such automotive radiator described above has a technical disadvantage. Namely, the super heated steam within the upper tank floods out from an annular sealing portion of the pressure valve toward whole orientations when the pressure valve is opened. The stream of flooded super heated steam, therefore, must be scrolling flow having the whole vectors. Since the connecting pipe is opened at only one point of the side wall of the tubular member, it must be very hard for such scrolling super heated steam flow to be introduced in the connecting pipe and to flow toward the reserve tank. The scrolling super heated steam flow should be remain within the tubular member so that the pressure within the tubular member must increase and it causes serious influence to the predetermined opening pressure of the pressure valve.